The BET (Bromodomain and Extra-Terminal) family of bromodomain containing proteins comprises 4 proteins (BRD2, BRD3, BRD4 and BRD-t) that share a conserved structural organization containing tandem N-terminal bromodomains capable of binding to acetylated lysine residues of histones and other proteins. BRD2, BRD3 and BRD4 are ubiquitously expressed while BRD-t is restricted to germ cells. BRD proteins play essential, but non-overlapping roles in regulating gene transcription and controlling cell growth. BET proteins are associated with large protein complexes including Mediator, PAFc and super elongation complex that regulate many aspects of gene transcription. BRD2 and BRD4 proteins have been shown to remain in complex with chromosomes during mitosis and are required to promote transcription of critical genes including cyclin D and c-Myc that initiate the cell cycle. Mochizuki et al., J. Biol. Chem. 2008, 283, 9040-9048. BRD4 is essential for recruiting the protein translational elongation factor B complex to the promoters of inducible genes resulting in the phosphorylation of RNA polymerase II and stimulating productive gene transcription and elongation. Jang et al., Mol. Cell, 2005, 19, 523-534. In some instances, a kinase activity of BRD4 may directly phosphorylate and activate RNA polymerase II. Devaiah et al., Proc. Nat. Acad. Sci., USA. 2012, 109, 6927-6932. Cells lacking BRD4 show impaired progression through cell cycle. BRD2 and BRD3 are reported to associate with histones along actively transcribed genes and may be involved in facilitating transcriptional elongation. Leroy et al., Mol. Cell, 2008, 30, 51-60. In addition to acetylated histones, BET proteins have been shown to bind selectively to acetylated transcription factors including the RelA subunit of NF-kB and GATA1 thereby directly regulating the transcriptional activity of these proteins to control expression of genes involved in inflammation and hematopoietic differentiation. Huang et al., Mol. Cell Biol., 2009, 29, 1375-1387; Lamonica et al., Proc. Nat. Acad. Sci., USA, 2011, 108, E159-168.
A recurrent translocation involving NUT (nuclear protein in testes) with BRD3 or BRD4 to form a novel fusion oncogene, BRD-NUT, is found in a highly malignant form of epithelial neoplasia. French et al., Cancer Res., 2003, 63, 304-307; French et al., J. Clin. Oncol., 2004, 22, 4135-4139. Selective ablation of this oncogene restores normal cellular differentiation and reverses the tumorigenic phenotype. Filippakopoulos et al., Nature, 2010, 468, 1068-1073. Genetic knockdown of BRD2, BRD3 and BRD4 has been shown to impair the growth and viability of a wide range of hematological and solid tumor cells. Zuber et al., Nature, 2011, 478, 524-528; Delmore et al., Cell, 2011, 146, 904-917. Aside from a role in cancer, BET proteins regulate inflammatory responses to bacterial challenge, and a BRD2 hypomorph mouse model showed dramatically lower levels of inflammatory cytokines and protection from obesity induced diabetes. Wang et al., Biochem. J., 2009, 425, 71-83; Belkina et al., J. Immunol. 102838, online publication before print, Feb. 18, 2013. In addition, some viruses make use of these BET proteins to tether their genomes to the host cell chromatin, as part of the process of viral replication or use BET proteins to facilitate viral gene transcription and repression. You et al., Cell, 2004, 117, 349-60; Zhu et al., Cell Reports, 2012, 2, 807-816.
Inhibitors of BET proteins are in current development. Exemplary BET protein inhibitors are disclosed in, for example, U.S. Pat. App. Pub. Nos. 2014/0275030; 2015/0011540; 2015/0148375; 2015/0148342; 2015/0148372; and 2015/0175604. An example of BET protein inhibitor is (4S)-7-(3,5-dimethylisoxazol-4-yl)-4-pyridin-2-yl-4,5-dihydroimidazo[1,5,4-de][1,4]benzoxazin-2(M)-one which is described in U.S. Pat. App. Pub. No. 2014/0275030. While certain inhibitors of BET proteins are in the literature, there remains a need for new solid forms of these inhibitors having suitable properties useful in the manufacture of safe, effective, high quality drug products. The present invention described herein is directed toward this end.